Biodegradable Set Retarder For A Cement Composition

ABSTRACT

Compositions and methods are directed to a cement composition for use in a subterranean formation. In an embodiment the cement composition comprises: (A) cement; (B) water; and (C) a polymer, wherein the polymer: (i) consists essentially of a monomer or monomers selected from the group consisting of acrylic acid, esters of acrylic acid, maleic acid, methacrylic acid, esters of methacrylic acid, itaconic acid, fumeric acid, citraconic acid, mesoconic acid, and any alkali metal, alkaline earth metal, or ammonium salt of any of the foregoing, and any combination of any of the foregoing; (ii) has the following characteristics: (a) is water soluble; and (b) is biodegradable; and (iii) is capable of providing: (a) a thickening time of at least 2 hours for a test composition maintained under a temperature condition of 190° F. and a pressure of 5,160 psi; and (b) an initial setting time of less than 24 hours for the test composition maintained under a temperature condition of 217° F. and a pressure of 3,000 psi, wherein the test composition consists of 860 grams of Class-H Portland cement, 325 grams of deionized water, and 0.4% by weight of the cement of the polymer. In another embodiment the method comprises the steps of: (A) introducing the cement composition into the subterranean formation; and (B) allowing the cement composition to set after introduction into the subterranean formation.

FIELD OF THE INVENTION

The invention is directed to a cement composition for use in asubterranean formation and a method for cementing a subterraneanformation. In certain embodiments, the subterranean formation containsan oil or gas well.

SUMMARY OF THE INVENTION

According to an embodiment, a cement composition comprises: (A) cement;(B) water; and (C) a polymer, wherein the polymer: (i) consistsessentially of a monomer or monomers selected from the group consistingof acrylic acid, esters of acrylic acid, maleic acid, methacrylic acid,esters of methacrylic acid, itaconic acid, fumeric acid, citraconicacid, mesoconic acid, and any alkali metal, alkaline earth metal, orammonium salt of any of the foregoing, and any combination of any of theforegoing; (ii) has the following characteristics: (a) is water soluble;and (b) is biodegradable; and (iii) is capable of providing: (a) athickening time of at least 2 hours for a test composition maintainedunder a temperature condition of 190° F. and a pressure of 5,160 psi;and (b) an initial setting time of less than 24 hours for the testcomposition maintained under a temperature condition of 217° F. and apressure of 3,000 psi, wherein the test composition consists of 860grams of Class-H Portland cement, 325 grams of deionized water, and 0.4%by weight of the cement of the polymer.

According to another embodiment, a method for cementing in asubterranean formation comprises the steps of: (A) introducing thecement composition into the subterranean formation; and (B) allowing thecement composition to set after introduction into the subterraneanformation.

As used herein, the words “comprise,” “have,” “include,” and allgrammatical variations thereof are each intended to have an open,non-limiting meaning that does not exclude additional elements or steps.

As used herein, the words “consisting essentially of,” and allgrammatical variations thereof are intended to limit the scope of aclaim to the specified materials or steps and those that do notmaterially affect the basic and novel characteristic(s) of the claimedinvention. For example, the polymer consists essentially of a monomer ormonomers selected from the group consisting of acrylic acid, esters ofacrylic acid, maleic acid, methacrylic acid, esters of methacrylic acid,itaconic acid, fumeric acid, citraconic acid, mesoconic acid, and anyalkali metal, alkaline earth metal, or ammonium salt of any of theforegoing, and any combination of any of the foregoing. The polymer cancontain other monomers so long as the presence of the other monomersdoes not materially affect the basic and novel characteristics of theclaimed invention, i.e., so long as the polymer is water soluble and isbiodegradable.

The polymer as explained above consisting essentially of a monomer orthe monomers selected from the group consisting of acrylic acid, estersof acrylic acid, maleic acid, methacrylic acid, esters of methacrylicacid, itaconic acid, fumeric acid, citraconic acid, mesoconic acid, andany alkali metal, alkaline earth metal, or ammonium salt of any of theforegoing, and any combination of any of the foregoing can be graftedonto a biodegradable backbone such as gelatin, lignin, tannin, chitosanand cellulose. Preferably the polymer can be grafted onto a gelatinbackbone.

It should also be understood that, as used herein, “first,” “second,”and “third,” are assigned arbitrarily and are merely intended todifferentiate between two or more monomers, fluids, etc., as the casemay be, and does not indicate any sequence. Furthermore, it is to beunderstood that the mere use of the term “first” does not require thatthere be any “second,” and the mere use of the word “second” does notrequire that there be any “third,” etc.

BRIEF DESCRIPTION OF THE DRAWING

The features and advantages of the inventions will be more readilyappreciated when considered in conjunction with the accompanyingdrawing. The accompanying drawing is incorporated into the specificationto help illustrate examples of certain embodiments. The drawing is notto be construed as limiting the invention.

The experiments for the data contained in the drawing were performed ona cement composition, having a density of 16.4 pounds per gallon (ppg),containing: 5.48 gallons of deionized water; Class-H cement; SSA-2™strength stabilizer at a concentration of 35% by weight of the cement(bwc); HALAD®344 fluid loss additive at a concentration of 0.5% bwc; anda polymer according to the invention. In certain experiments, thepolymer was PAA/MA (a sodium salt copolymer of acrylic acid and maleicanhydride) having an average molecular weight of 4,500 and a mole ratioof 80:20). In certain experiments, the polymer was PAA (a homopolymer ofacrylic acid). The drawing includes the following figures:

FIG. 1 is a graph of thickening time in minutes (min) versus temperaturein Fahrenheit (° F.) for the cement composition at a pressure of 10,200psi wherein the polymer was PAA/MA at a concentration of 0.4% bwc.

FIG. 2 is a graph of thickening time (min) versus temperature (° F.) forthe cement composition at a pressure of 10,200 psi wherein the polymerwas PAA (average molecular weight in the range of about 3,000 to about4,000) at a concentration of 0.4% bwc.

FIG. 3 is a graph of thickening time (min) versus concentration of thepolymer PAA (% bwc) (average molecular weight in the range of about3,000 to about 4,000) for the cement composition at a temperature of217° F. and a pressure of 10,200 psi.

FIG. 4 is a graph of temperature (° F.) and consistency (Be) versus time(hrs:min) for the cement composition heated to a temperature of 350° F.and a pressure of 10,200 psi wherein the polymer was PAA (averagemolecular weight in the range of about 3,000 to about 4,000) at aconcentration of 1.0% bwc.

FIG. 5 is a graph of thickening time (min) versus concentration ofsodium chloride (NaCl) (% by weight of water) for the cement compositionat a temperature of 217° F. and a pressure of 10,200 psi wherein thepolymer was PAA (average molecular weight in the range of about 3,000 toabout 4,000) at a concentration of 0.4% bwc.

FIG. 6 is a graph of thickening time (min) versus concentration of PAA(% bwc) (average molecular weight of 1,200) for the cement compositionat a temperature of 245° F. and a pressure of 10,200 psi.

FIG. 7 is a graph of thickening time (min) versus temperature (° F.) forthe cement composition at a pressure of 10,200 psi wherein the polymerwas the homopolymer PAA (average molecular weight of 1,200) at aconcentration of 0.4% bwc.

DETAILED DESCRIPTION OF THE INVENTION

Oil and gas hydrocarbons are naturally occurring in some subterraneanformations. A subterranean formation containing oil or gas is sometimesreferred to as a reservoir. A reservoir may be located under land or offshore. Reservoirs are typically located in the range of a few hundredfeet (shallow reservoirs) to a few tens of thousands of feet (ultra-deepreservoirs). In order to produce oil or gas, a well is drilled into asubterranean formation.

According to certain embodiments, the subterranean formation contains anoil or gas well. As used herein, a “well” includes at least one wellboredrilled into a subterranean formation, which may be a reservoir oradjacent to a reservoir. A wellbore can have vertical and horizontalportions, and it can be straight, curved, or branched. As used herein,the term “wellbore” refers to a wellbore itself, including any uncased,open-hole portion of the wellbore. A near-wellbore region is thesubterranean material and rock of the subterranean formation surroundingthe wellbore. As used herein, a “well” also includes the near-wellboreregion. The near-wellbore region is generally considered to be theregion within about 100 feet of the wellbore. As used herein, “into awell” means and includes into any portion of the well, including intothe wellbore or into the near-wellbore region via the wellbore.

As used herein, a “fluid” is a substance having a continuous phase andthat tends to flow and to conform to the outline of its container whenthe substance is tested at a temperature of 71° F. and a pressure of oneatmosphere. An example of a fluid is a liquid or gas. As used herein, a“fluid” can have more than one distinct phase. For example, a “fluid”can be or include a slurry, which is a suspension of solid particles ina continuous liquid phase; it can be or include an emulsion, which is asuspension of two or more immiscible liquids where droplets of at leastone liquid phase are dispersed in a continuous liquid phase of another;or it can be or include a foam, which is a suspension or dispersion ofgas bubbles in a continuous liquid phase.

In order to produce oil or gas, a wellbore is drilled into or near asubterranean formation. The wellbore may be an open hole or cased hole.In an open-hole wellbore, a tubing string is placed into the wellbore.The tubing string allows fluids to be introduced into or flowed from aremote portion of the wellbore. In a cased hole, a casing is placed intothe wellbore that can contain a tubing string. In an open hole, thespace between the wellbore and the outside of a tubing string is anannulus. In a cased hole, the space between the wellbore and the outsideof the casing is an annulus. Also, in a cased hole, there may be anannulus between the tubing string and the inside of the casing.

As used herein, a “cement composition” is a mixture of at least cementand water, and the cement composition can include additives. As usedherein, the term “cement” means a dry powder substance that acts as abinder to bind other materials together. During well completion, it iscommon to introduce a cement composition into an annulus in thewellbore. For example, in a cased hole, the cement composition is placedand allowed to set in the annulus between the wellbore and the casing inorder to stabilize and secure the casing in the wellbore. By cementingthe casing in the wellbore, fluids are prevented from flowing into theannulus. Consequently, oil or gas can be produced in a controlled mannerby directing the flow of oil or gas through the casing and into thewellhead. Cement compositions can also be used in well-pluggingoperations or gravel-packing operations.

During cementing operations, it is necessary for the cement compositionto remain pumpable during introduction into the well and until thecomposition is situated in the portion of the well to be cemented. Afterthe cement composition has reached the portion of the well to becemented, the cement composition ultimately sets. A cement compositionthat thickens too quickly while being pumped can damage pumpingequipment or block tubing or pipes, and a cement composition that setstoo slowly can cost time and money while waiting for the composition toset.

As used herein, the “thickening time” is how long it takes for a cementcomposition to become unpumpable under specified temperature andpressure conditions. The pumpability of a cement composition is relatedto the consistency of the composition. The consistency of a cementcomposition is measured in Bearden units of consistency (Be), adimensionless unit with no direct conversion factor to the more commonunits of viscosity. As used herein, a cement composition becomes“unpumpable” when the consistency of the composition reaches 70 Bc. Asused herein, the consistency of a cement composition is measured asfollows. The water is added to a mixing container and the container isthen placed on a mixer base. The motor of the base is then turned on andmaintained at 4,000 revolutions per minute (rpm). The cement and anyother ingredients are added to the container at a uniform rate in notmore than 15 seconds (s). After all the cement and any other ingredientshave been added to the water in the container, a cover is then placed onthe container, and the cement composition is mixed at 12,000 rpm (+/−500rpm) for 35 s (+/−1 s). The cement composition is then placed in thetest cell of a High-Temperature, High-Pressure (HTHP) consistometer,such as a Fann Model 275 or a Chandler Model 8240. The cementcomposition is ramped up to the specified temperature and pressurecondition and is maintained under the temperature and pressurecondition. Consistency measurements are taken continuously until thecement exceeds 70 Bc.

A cement composition can develop compressive strength. Cementcomposition compressive strengths can vary from 0 psi to over 10,000psi. As used herein, “compressive strength” is measured at a specifiedtime after the composition has been mixed and the composition ismaintained under specified temperature and possibly pressure conditions.For example, compressive strength can be measured at a time in the rangeof about 24 to about 48 hours after the composition is mixed and thecomposition is maintained at a temperature of 217° F. Compressivestrength can be measured by either a destructive method ornon-destructive method.

The destructive method physically tests the strength of cementcomposition samples at various points in time by crushing the samples ina compression-testing machine. The compressive strength is calculatedfrom the failure load divided by the cross-sectional area resisting theload and is reported in units of pound-force per square inch (psi) ormegapascals (MPa).

The non-destructive method continually measures estimated compressivestrength of a cement composition sample throughout the test period byutilizing a non-destructive sonic device such as an Ultrasonic CementAnalyzer (UCA) available from Fann Instruments in Houston, Tex. As usedherein, the “compressive strength” of a cement composition is measuredutilizing an Ultrasonic Cement Analyzer as follows. The water is addedto a mixing container and the container is then placed on a mixer base.The motor of the base is then turned on and maintained at 4,000revolutions per minute (rpm). The cement and any other ingredients areadded to the container at a uniform rate in not more than 15 seconds(s). After all the cement and any other ingredients have been added tothe water in the container, a cover is then placed on the container, andthe cement composition is mixed at 12,000 rpm (+/−500 rpm) for 35 s(+/−1 s). The cement composition is placed in an Ultrasonic CementAnalyzer and heated to the specified temperature condition andpressurized to the specified pressure condition. The UCA continuallymeasures the transit time of the acoustic signal through the sample. TheUCA device contains preset algorithms that correlate transit time tocompressive strength. The UCA reports the compressive strength of thecement composition in psi.

The compressive strength of a cement composition can be used to indicatewhether the cement composition has set. A cement composition “initiallysets.” As used herein, a cement composition is considered “initiallyset” when the cement composition develops a compressive strength of 50psi using the non-destructive compressive strength method at atemperature condition of 217° F. and a pressure of 3,000 psi. As usedherein, the “initial setting time” is the difference in time betweenwhen the cement is added to the water and when the composition isinitially set.

As used herein, the term “set” is intended to mean the process ofbecoming hard or solid by curing. It may take up to 72 hours for acement composition to set. Some cement compositions can continue todevelop a compressive strength greater than 50 psi over the course ofseveral days. The compressive strength of a cement composition can reachover 10,000 psi.

A set retarder can be added to a cement composition to help increase thethickening time of the cement composition such that the cementcomposition remains pumpable for a desired time. The thickening time isproportional to the setting time, i.e., the longer the thickening time,the longer the setting time will be. Therefore, a set retarder can beadded to a cement composition to help increase the setting time of thecement composition. However, if a set retarder is in too-high aconcentration, the cement composition may never set. Therefore, the setretarder also can be used in a concentration such that the cementcomposition sets in a desired time.

Conventional set retarders have been used to delay the setting time ofcement compositions. Examples of conventional set retarders aredisclosed in U.S. Pat. No. 7,004,256 issued Feb. 28, 2006 to Chatterjiet al., which is incorporated by reference in its entirety. Anotherexample of a conventional set retarder is a copolymer formed from amonomer of 2-acrylamido-2-methylpropane sulfonic acid (“AMPS”). Oneexample of a conventional AMPS set retarder is “SCR-100™”, availablefrom Halliburton Energy Services, Inc. in Duncan, Okla.

A polymer is a large molecule composed of repeating units typicallyconnected by covalent chemical bonds. The number of repeating units of apolymer can range from approximately 10 to greater than 10,000. Thenumber of repeating units of a polymer is referred to as the chainlength of the polymer. A polymer is formed from the polymerizationreaction of monomers. A polymer formed from one type of monomer iscalled a homopolymer. A copolymer is formed from two or more differenttypes of monomers. In the polymerization reaction, the monomers aretransformed into the repeating units of a polymer. The conditions of thepolymerization reaction can be adjusted to help control the averagenumber of repeating units (the average chain length) of a polymer. Apolymer also has an average molecular weight, which is directly relatedto the average chain length of the polymer. The average molecular weightof a polymer has an impact on some of the physical characteristics of apolymer, for example, its solubility in water and its biodegradability.

For a copolymer, each of the monomers will be repeated a certain numberof times (number of repeating units). The average molecular weight for acopolymer can be expressed as follows:

Avg. molecular weight=*(M.W.m ₁*RUm ₁)+(M.W.m ₂*RUm ₂)

where M.W.m₁ is the molecular weight of the first monomer; RU m₁ is thenumber of repeating units of the first monomer; M.W.m₂ is the molecularweight of the second monomer; and RU m₂ is the number of repeating unitsof the second monomer. Of course, a terpolymer would include threemonomers, a tetra polymer would include four monomers, and so on.

For a copolymer made from two monomers, the mole ratio is the ratio ofthe moles of the first monomer to the moles of the second monomer. Forexample, a copolymer can have a mole ratio of 50:50, which means that,for every one mole of the first monomer, there is one mole of the secondmonomer. By way of another example, a mole ratio of 80:20 means that,for every 4 moles of the first monomer, there is one mole of the secondmonomer.

In a copolymer, the repeating units for each of the monomers can bearranged in various ways along the polymer chain. For example, therepeating units can be random, alternating, periodic, or block.

Some polymer conventional set retarders do not increase the thickeningat least 2 hours in high-temperature wells. As used herein, ahigh-temperature well is a well with a bottomhole temperature in therange of 150° F. to 500° F. The bottomhole temperature refers to thedownhole temperature at the portion of the well to be cemented. In orderto make some polymer conventional set retarders effective inhigh-temperature wells, the molecular weight of the polymer can beincreased (usually to a molecular weight of greater than 10,000).

Some nations have implemented new environmental regulations which setstandards for the biodegradability of wellbore fluids (especially foroff-shore drilling). Biodegradability is the process by which complexmolecules are broken down by microorganisms to produce simplercompounds. However, as the molecular weight of a polymer increases, itsbiodegradability tends to decrease. Thus, in most of the cases, highmolecular weight polymers may not satisfy the new environmentalregulations, and, thus, the polymers may not be able to be used. As usedherein, a high molecular weight polymer is a polymer that has an averagemolecular weight of greater than 10,000. As used herein, a low molecularweight polymer is a polymer that has an average molecular weight of lessthan 10,000.

Also, in general, as the molecular weight of a polymer increases, itssolubility decreases. As a result, some high molecular weight polymersare generally water-swellable; whereas, some low molecular weightpolymers are generally water soluble. As used herein, a polymer is“water soluble” if at least 1 part by weight of the polymer dissolves in5 parts by weight of deionized water at a temperature of 80° F.

As used herein, a polymer is considered “biodegradable” if the polymerpasses a ready biodegradability test or an inherent biodegradabilitytest. It is preferred that a polymer is first tested for readybiodegradability and only if the polymer does not pass the readybiodegradability test then the polymer is then tested for inherentbiodegradability. It is believed that the polymer according to theinvention will pass the ready biodegradability or inherentbiodegradability test.

In accordance with Organisation for Economic Co-operation andDevelopment (OECD) guidelines, the following 6 tests permit thescreening of chemicals for ready biodegradability. As used herein, apolymer showing more than 60% biodegradability in 28 days according toany one of the 6 ready biodegradability tests is considered a pass levelfor classifying it as “readily biodegradable,” and it may be assumedthat the polymer will undergo rapid and ultimate degradation in theenvironment. The 6 tests are: 301 A: DOC Die-Away; 301 B: CO2 Evolution(Modified Sturm Test); 301 C: MITI (I) (Ministry of International Tradeand Industry, Japan); 301 D: Closed Bottle; 301 E: Modified OECDScreening; and 301 F: Manometric Respirometry.

1. For the 301A test, a measured volume of inoculated mineral medium,containing 10 mg to 40 mg dissolved organic carbon per liter (DOC/1)from the polymer as the nominal sole source of organic carbon, isaerated in the dark or diffuse light at 22±2° C. Degradation is followedby DOC analysis at frequent intervals over a 28-day period. The degreeof biodegradation is calculated by expressing the concentration of DOCremoved (corrected for that in the blank inoculum control) as apercentage of the concentration initially present. Primarybiodegradation may also be calculated from supplemental chemicalanalysis for parent compound made at the beginning and end ofincubation.

2. For the 301 B test, a measured volume of inoculated mineral medium,containing 10 mg to 20 mg DOC or total organic carbon per liter from thepolymer as the nominal sole source of organic carbon is aerated by thepassage of carbon dioxide-free air at a controlled rate in the dark orin diffuse light. Degradation is followed over 28 days by determiningthe carbon dioxide produced. The CO₂ is trapped in barium or sodiumhydroxide and is measured by titration of the residual hydroxide or asinorganic carbon. The amount of carbon dioxide produced from the testsubstance (corrected for that derived from the blank inoculum) isexpressed as a percentage of ThCO₂. The degree of biodegradation mayalso be calculated from supplemental DOC analysis made at the beginningand end of incubation.

3. For the 301C test, the oxygen uptake by a stirred solution, orsuspension, of the polymer in a mineral medium, inoculated withspecially grown, unadapted micro-organisms, is measured automaticallyover a period of 28 days in a darkened, enclosed respirometer at 25+/−1°C. Evolved carbon dioxide is absorbed by soda lime. Biodegradation isexpressed as the percentage oxygen uptake (corrected for blank uptake)of the theoretical uptake (ThOD). The percentage primary biodegradationis also calculated from supplemental specific chemical analysis made atthe beginning and end of incubation, and optionally ultimatebiodegradation by DOC analysis.

4. For the 301D test, a solution of the polymer in mineral medium,usually at 2-5 milligrams per liter (mg/l), is inoculated with arelatively small number of micro-organisms from a mixed population andkept in completely full, closed bottles in the dark at constanttemperature. Degradation is followed by analysis of dissolved oxygenover a 28 day period. The amount of oxygen taken up by the microbialpopulation during biodegradation of the test substance, corrected foruptake by the blank inoculum run in parallel, is expressed as apercentage of ThOD or, less satisfactorily COD.

5. For the 301E test, a measured volume of mineral medium containing 10to 40 mg DOC/l of the polymer as the nominal sole source of organiccarbon is inoculated with 0.5 ml effluent per liter of medium. Themixture is aerated in the dark or diffused light at 22+2° C. Degradationis followed by DOC analysis at frequent intervals over a 28 day period.The degree of biodegradation is calculated by expressing theconcentration of DOC removed (corrected for that in the blank inoculumscontrol) as a percentage of the concentration initially present. Primarybiodegradation may also be calculated from supplemental chemicalanalysis for the parent compound made at the beginning and end ofincubation.

6. For the 301F test, a measured volume of inoculated mineral medium,containing 100 mg of the polymer per liter giving at least 50 to 100 mgThOD/1 as the nominal sole source of organic carbon, is stirred in aclosed flask at a constant temperature (+1° C. or closer) for up to 28days. The consumption of oxygen is determined either by measuring thequantity of oxygen (produced electrolytically) required to maintainconstant gas volume in the respirometer flask or from the change involume or pressure (or a combination of the two) in the apparatus.Evolved carbon dioxide is absorbed in a solution of potassium hydroxideor another suitable absorbent. The amount of oxygen taken up by themicrobial population during biodegradation of the test substance(corrected for uptake by blank inoculum, run in parallel) is expressedas a percentage of ThOD or, less satisfactorily, COD. Optionally,primary biodegradation may also be calculated from supplemental specificchemical analysis made at the beginning and end of incubation, andultimate biodegradation by DOC analysis.

In accordance with OECD guidelines, the following three tests permit thescreening of chemicals for inherent biodegradability. As used herein, apolymer with a biodegradation or biodegradation rate of >20% is regardedas “inherently primary biodegradable.” A polymer with a biodegradationor biodegradation rate of >70% is regarded as “inherently ultimatebiodegradable.” A polymer passes the inherent biodegradability test ifthe polymer is either regarded as inherently primary biodegradable orinherently ultimate biodegradable when tested according to any one ofthe 3 tests. The 3 tests are: 302 A-1981 Modified SCAS Test; 302 B-1992Zahn-Wellens Test; and 302 C-1981 Modified MITI Test. Inherentbiodegradability refers to tests which allow prolonged exposure of thetest compound to microorganisms, a more favorable test compound tobiomass ratio, and chemical or other conditions which favorbiodegradation.

1. For the 302A test, activated sludge from a sewage treatment plant isplaced in an aeration (SCAS) unit. The polymer and settled domesticsewage are added, and the mixture is aerated for 23 hours. The aerationis then stopped, the sludge allowed to settle and the supernatant liquoris removed. The sludge remaining in the aeration chamber is then mixedwith a further aliquot of the polymer and sewage and the cycle isrepeated. Biodegradation is established by determination of thedissolved organic carbon content of the supernatant liquor. This valueis compared with that found for the liquor obtained from a control tubedosed with settled sewage only.

2. For the 302B test, a mixture containing the polymer, mineralnutrients, and a relatively large amount of activated sludge in aqueousmedium is agitated and aerated at 20° C. to 25° C. in the dark or indiffuse light for up to 28 days. A blank control, containing activatedsludge and mineral nutrients but no polymer, is run in parallel. Thebiodegradation process is monitored by determination of DOC (or COD(2))in filtered samples taken at daily or other time intervals. The ratio ofeliminated DOC (or COD), corrected for the blank, after each timeinterval, to the initial DOC value is expressed as the percentagebiodegradation at the sampling time. The percentage biodegradation isplotted against time to give the biodegradation curve.

3. For the 302C test, an automated closed-system oxygen consumptionmeasuring apparatus (BOD-meter) is used. The polymer to be tested isinoculated in the testing vessels with micro-organisms. During the testperiod, the biochemical oxygen demand is measured continuously by meansof a BODmeter. Biodegradability is calculated on the basis of BOD andsupplemental chemical analysis, such as measurement of the dissolvedorganic carbon concentration, concentration of residual chemicals, etc.

It has been discovered that a water-soluble, biodegradable polymer ofacrylic acid, maleic acid, methacrylic acid, itaconic acid, fumericacid, citraconic acid, mesoconic acid, and any combination thereof canbe used as a set retarder. Another advantage is that the polymer canincrease the thickening time by approximately 20% compared toconventional set retarders at the same concentration in the range ofabout 0.1% to about 5% by weight of cement and a temperature of 150° F.and a pressure of 5,160 psi. Yet another advantage to the polymer is itis salt tolerant. As used herein, “salt tolerant” means that a cementcomposition containing 325 g of deionized water, 860 g of Class-HPortland Cement, 0.4% bwc of the polymer, and sodium chloride (NaCl) ata concentration of 30% by weight of the water, at a constant temperatureof 125° F. and a pressure of 5,160 psi, will have a thickening time ofat least 2 hours. Thus, the polymer is water soluble, is biodegradable,is a set retarder, can be used in a lower concentration compared toconventional set retarders, can be used in the presence of salt, and ismore cost effective compared to conventional set retarders.

According to an embodiment, a cement composition for use in asubterranean formation is provided. The cement composition comprises:(A) cement; (B) water; and (C) a polymer, wherein the polymer: (i)consists essentially of a monomer or monomers selected from the groupconsisting of acrylic acid, esters of acrylic acid, maleic acid,methacrylic acid, esters of methacrylic acid, itaconic acid, fumericacid, citraconic acid, mesoconic acid, and any alkali metal, alkalineearth metal, or ammonium salt of any of the foregoing, and anycombination of any of the foregoing; (ii) has the followingcharacteristics: (a) is water soluble; and (b) is biodegradable; and(iii) is capable of providing: (a) a thickening time of at least 2 hoursfor a test composition maintained under a temperature condition of 190°F. and a pressure of 5,160 psi; and (b) an initial setting time of lessthan 24 hours for the test composition maintained under a temperaturecondition of 217° F. and a pressure of 3,000 psi, wherein the testcomposition consists of 860 grams of Class-H Portland cement, 325 gramsof deionized water, and 0.4% by weight of the cement of the polymer.

According to another embodiment, a method for cementing in asubterranean formation is provided. The method comprises the steps of:(A) introducing the cement composition into the subterranean formation;and (B) allowing the cement composition to set after introduction intothe subterranean formation.

The cement composition includes cement. Preferably, the cement isPortland Cement Type I, II, or III. Preferably, the cement is Class Acement, Class C cement, Class G cement, or Class H cement. Preferably,the cement composition has a density in the range of about 9 to about 22pounds per gallon (ppg).

The cement composition includes water. The water can be selected fromthe group consisting of freshwater, brackish water, and saltwater, inany combination thereof in any proportion. The cement composition alsocan include salt. Preferably, the salt is selected from sodium chloride,calcium chloride, calcium bromide, potassium chloride, potassiumbromide, magnesium chloride, and any combination thereof in anyproportion. Preferably, the salt is in a concentration in the range ofabout 0.1% to about 40% by weight of the water.

The cement composition includes a polymer, wherein the polymer consistsessentially of a monomer or monomers selected from the group consistingof acrylic acid, esters of acrylic acid, maleic acid, methacrylic acid,esters of methacrylic acid, itaconic acid, fumeric acid, citraconicacid, mesoconic acid, and any alkali metal, alkaline earth metal, orammonium salt of any of the foregoing, and any combination of any of theforegoing. The polymer can be grafted onto a biodegradable backbone suchas gelatin, lignin, tannin, chitosan, and cellulose. If the polymer isgrafted onto a biodegradable backbone, then, preferably, the backbone isgelatin. Preferably, the monomer or monomers are not AMPS orlignosulfonate and its salts. The polymer can also be an alkali metal,an alkaline earth metal, or an ammonium salt. The monomer or monomerscan be neutralized prior to the polymerization reaction. The polymer canbe neutralized or at least partially neutralized after thepolymerization reaction. An alkali metal polymer means the product thatresults from a reaction of an acid with a Group I metal (which includelithium, sodium, potassium, rubidium, cesium, and francium). An exampleof an alkali metal polymer is acrylic acid sodium salt. An alkalineearth metal polymer means the product that results from a reaction of anacid with a Group IIA metal (which includes beryllium, magnesium,calcium, strontium, barium, and radium). An example of an alkaline earthmetal polymer is calcium polyacrylate. An ammonium salt polymer meansthe product that results from a reaction of an acid and ammonia. Anexample of an ammonium salt polymer is ammonium polyacrylate.

Preferably, the esters of acrylic acid are selected from acrylate andbutyl acrylate. Preferably, the ester of methacrylic acid ismethacrylate.

If the polymer is a copolymer, then the monomers can be arranged asrandom, alternating, periodic, or block. Preferably, the monomers arearranged as random.

Preferably, for a homopolymer, the monomers are selected from acrylicacid, maleic anhydride, itaconic acid, and methacrylic acid. Morepreferably, for a homopolymer, the monomer is acrylic acid, and thehomopolymer is a sodium salt. Preferably, for a copolymer, one of themonomers is acrylic acid, and the other monomer is selected from maleicanhydride, acrylamide, methacrylic acid, and butyl acrylate. Morepreferably, for a copolymer, the monomers are acrylic acid and maleicanhydride, and the copolymer is a sodium salt. Preferably, for aterpolymer, the monomers are: acrylic acid, maleic anhydride, andacrylamide; acrylic acid, methacrylic acid, and butyl acrylate; andacrylic acid, maleic anhydride, and itaconic acid. More preferably, fora terpolymer, the monomers are acrylic acid, maleic anhydride, andacrylamide, and the terpolymer is a sodium salt.

Preferably, the polymer is in at least a sufficient concentration suchthat the cement composition has a thickening time of at least 3 hoursmaintained under a temperature condition of 217° F. and a pressure of10,200 psi. Preferably, the polymer is in a concentration equal to orless than a sufficient concentration such that the cement compositionsets in less than 48 hours maintained under a temperature condition of217° F. and a pressure of 3,000 psi. Preferably, the polymer is in aconcentration in the range of about 0.05% to about 10% by weight of thecement. More preferably, the polymer is in a concentration in the rangeof about 0.1° A to about 2% by weight of the cement. One of skill in theart will be able to determine the concentration of the polymer needed inorder to achieve the desired thickening time, for example, based on theamount of salt which may be present in the water and the bottom-holetemperature of the well, among other specific conditions of the well.

The polymer has an average molecular weight such that the polymer hasthe following characteristics: is water soluble and is biodegradable.Preferably, the polymer has an average chain length in the range of 5 to80. More preferably, the polymer has an average chain length of 10 to60. Preferably, the polymer has an average molecular weight in the rangeof about 500 to about 5,000. More preferably, the polymer has an averagemolecular weight in the range of about 600 to about 3,500. Mostpreferably, the polymer has an average molecular weight in the range ofabout 800 to about 2,000. Preferably, for a copolymer with two monomers,the monomers are in a mole ratio of 50:50. More preferably, the monomersare in a mole ratio of 80:20. Most preferably, the monomers are in amole ratio of 90:10. Preferably, for a terpolymer, the monomers are in amole ratio of 40:30:30. More preferably, the monomers are in a moleratio of 60:20:20. Preferably, one of the monomers is acrylic acid, andthe acrylic acid is in the highest mole ratio compared to the othermonomers. More preferably, the highest mole ratio monomer is acrylicacid, and the lowest mole ratio monomer from the above-listed group ismaleic anhydride.

Preferably, the cement composition has a thickening time of at least 3hours maintained under a temperature condition of 217° F. and a pressureof 10,200 psi. More preferably, the cement composition has a thickeningtime in the range of about 4 to about 10 hours maintained under atemperature condition of 217° F. and a pressure of 10,200 psi. Some ofthe variables that can affect the thickening time of the cementcomposition include the concentration of the polymer, the concentrationof any salt present in the cement composition, and the bottomholetemperature of the well. Preferably, the cement composition sets in lessthan 48 hours maintained under a temperature condition of 217° F. and apressure of 3,000 psi. More preferably, the cement composition sets inless than 24 hours maintained under a temperature condition of 217° F.and a pressure of 3,000 psi. Most preferably, the cement compositionsets at a time in the range of about 8 to about 24 hours maintainedunder a temperature condition of 217° F. and a pressure of 3,000 psi.

Preferably, the cement composition has a compressive strength of atleast 400 psi when tested at 24 hours and maintained under a temperaturecondition of 217° F. and a pressure of 3,000 psi. More preferably, thecement composition has a compressive strength in the range of 400 to10,000 psi when tested at 24 hours and maintained under a temperaturecondition of 217° F. and a pressure of 3,000 psi.

The cement composition also can include at least one additional setretarder to help control the thickening time of the cement composition.Preferably, any additional set retarder is also biodegradable.

The cement composition can include other additives suitable for use insubterranean cementing operations. Examples of such additives include,but are not limited to, strength-retrogression additives, setaccelerators, set retarders, weighting agents, lightweight additives,gas-generating additives, mechanical property enhancing additives,lost-circulation materials, filtration-control additives, dispersants,fluid loss control additives, defoaming agents, foaming agents,thixotropic additives, nano-particles, and combinations thereof.Preferably, any other additives are also biodegradable. For example, thecement composition can include a strength-retrogression additive. Thestrength-retrogression additive can be selected from the groupconsisting of course silica flour, fine silica flour, and anycombination thereof in any proportion. Preferably, the strengthstabilizer is in a concentration in the range of about 20% to about 50%by weight of the cement.

By way of another example, the cement composition can include a fluidloss additive. Suitable examples of fluid loss additives includeHALAD®344, HALAD®413, HALAD®400, HALAD®9, HALAD®14, HALAD®23,HALAD®100A, HALAD®300, HALAD®350, HALAD®400L, HALAD®600, HALAD®600LE+,HALAD®613, HALAD®766, FDP-703, Latex 2000, LAP-1, and LA-2, availablefrom Halliburton Energy Services, Inc. Preferably, the fluid lossadditive is in a concentration in the range of 0.1% to 4% by weight ofthe cement. The fluid loss additive can be biodegradable. Examples ofsuitable biodegradable fluid loss additives include HALAD®400 andHALAD®300.

By way of another example, the cement composition can include adispersant. Suitable examples of dispersants include CFRR2, CFR®3,CFR®SLE, CFR®6, CFR®8, FDP-701, and FDP-C-850, available fromHalliburton Energy Services, Inc. Preferably, the dispersant is in aconcentration in the range of 0.05% to 3% by weight of the cement.

The cement composition also can include a filler material. Suitableexamples of filler materials include, but are not limited to, fly ash,sand, clays, and vitrified shale. Preferably, the filler material is ina concentration in the range of about 5% to about 50% by weight of thecement.

The cement composition also can include other additives.Commercially-available examples of other additives include, but are notlimited to, SSA-1, SSA-2, High Dense-3, High Dense-4, Barite, Micromax,Silicalite, HGS-6000, HGS-4000, HGS-10000, Well life 665, Well life 809,and Well life 810, available from Halliburton Energy Services, Inc.

The method includes the step of introducing the cement composition intoa subterranean formation. Preferably, the subterranean formationcontains a well. Preferably, the portion of the well is a portion of theannulus. The step of introducing can be for the purpose of wellcompletion, primary or remedial cementing operations, squeeze cementing,well-plugging, or gravel packing. The cement composition is in apumpable state upon introduction into the subterranean formation. Themethod also includes the step of allowing the cement composition to setafter introduction into the subterranean formation. The method caninclude the additional steps of perforating, fracturing, or performingan acidizing treatment, after the step of allowing the cementcomposition to set.

For the method, preferably, the cement composition has a thickening timeof at least 3 hours at the bottomhole temperature and pressure of thewell. More preferably, the cement composition has a thickening time inthe range of about 4 to about 10 hours at the bottomhole temperature andpressure of the well. For example, one of skill in the art will be ableto select the thickening time based on the specific conditions of thewell (e.g., the length of the casing and the bottomhole temperature ofthe well). Some of the variables that can affect the thickening time ofthe cement composition include the concentration of the polymer, theconcentration of any salt present in the cement composition, and thebottomhole temperature of the well. Preferably, the cement compositionsets in less than 48 hours at the bottomhole temperature and pressure ofthe well. More preferably, the cement composition sets in less than 24hours at the bottomhole temperature and pressure of the well. Mostpreferably, the cement composition sets at a time in the range of about8 to about 24 hours at the bottomhole temperature and pressure of thewell. Preferably, the cement composition is used in a well having abottomhole temperature of at least 150° F. Preferably, the bottomholetemperature is in the range of 150° F. to 500° F. More preferably, thebottomhole temperature is in the range of about 180° F. to about 400° F.Most preferably, the bottomhole temperature is in the range of about180° F. to about 350° F. Preferably, the cement composition develops acompressive strength of at least 1,500 psi after the cement compositionhas been introduced into the well and is situated in the portion of wellto be cemented.

EXAMPLES

To facilitate a better understanding of the present invention, thefollowing examples of certain aspects of preferred embodiments aregiven. The following examples are not the only examples that could begiven according to the present invention and are not intended to limitthe scope of the invention.

Tables 1.1, 2.1, and 2.2 show the effect of the concentration of apolymer and temperature on thickening time. For Tables 1.1, 2.1, and2.2, several cement compositions, having a density of 16.4 pounds pergallon (ppg), were prepared. The cement compositions consisted of 5.48gallons of deionized water; Class-H cement; SSA-2™ strength stabilizerat a concentration of 35% by weight of the cement (bwc); HALAD®344 fluidloss additive at a concentration of 0.5% bwc; and varying concentrationsof a polymer according to the invention. Deionized water means waterthat has had its mineral ions removed, such as cations (e.g., sodium,calcium, iron, and copper) and anions (e.g., chloride and bromide). Apolymer conventional set retarder, SCR100™ is listed in both tables. InTable 1.1, a copolymer according to the invention (PAA/MA) (having anaverage molecular weight of 4,500 and a mole ratio of 80:20) was used invarying concentrations. PAA/MA is a sodium salt copolymer of acrylicacid and maleic anhydride. In one instance in Table 1.1 the watercontained salt, sodium chloride, in a concentration of 2.4% by weight ofthe water. In Tables 2.1 and 2.2, a homopolymer according to theinvention (PAA) was used in varying concentrations. PAA is a homopolymerof acrylic acid. In Table 2.1, the PAA had an average molecular weightin the range of about 3,000 to about 4,000. In Table 2.2, the PAA had anaverage molecular weight of 1,200. All of the cement compositions wereheated from an initial temperature of 70° F. to a maximum temperature ofat least 190° F. over the course of 44 minutes and then maintained atthat maximum temperature. The thickening time is the time it took forthe cement compositions to reach 70 Bc maintained under a pressurecondition of 10,200 psi. The consistency of the cement compositions weremeasured using a Fann Model 275 HTHP consistometer. The compressivestrength of the cement compositions, maintained under a pressurecondition of 3,000 psi, were measured at 24 or 48 hours after mixingusing an Ultrasonic Cement Analyzer and expressed in units of pounds persquare inch (psi). The initial setting time of the cement compositionswas the time it took for the cement compositions to reach 50 psi,maintained under a pressure condition of 3,000 psi, using an UltrasonicCement Analyzer.

TABLE 1.1 Set Conc. of Thickening Initial Setting Retarder set retarderTemperature Time Compressive Time Used (% bwc) (° F.) (hours:mins)Strength (psi) (hours:mins) 1 SCR-100 ™ 0.4 217 4 to 6 hrs. 2778 (24 hr)11:24 2 PAA/MA 0.4 217 6:54 2592 (24 hr) 12:32 3 PAA/MA 0.2 217 2:35 Notmeasured Not measured 4 PAA/MA 0.4 245 3:13 Not measured Not measured 5PAA/MA 0.4 300 1:06 Not measured Not measured 6 PAA/MA 0.4 245 2:12 Notmeasured Not measured (salt water) 7 PAA/MA 1.5 300 20.00+ Not measuredNot measured 8 PAA/MA 0.7 300 3:01 Not measured Not measured 9 PAA/MA0.8 300 4 hrs. Not measured Not measured

As can be seen in Table 1.1, for a fixed concentration of PAA/MA, thethickening time decreases with an increase in temperature andconcentration of salt. As can also be seen, PAA/MA performs comparablyto the polymer conventional set retarder SCR100™. As can also be seen inTable 1.1, for a fixed temperature, the thickening time increases withan increase in concentration of PAA/MA.

TABLE 2.1 Set Conc. of Thickening Initial Setting Retarder set retarderTemperature Time Compressive Time Used (% bwc) (° F.) (hours:mins)Strength (psi) (hours:mins) 1 SCR-100 ™ 0.4 217 4 to 6 hrs. 2778 11:24 2PAA 0.2 217 3:20 Not measured Not measured 3 PAA 0.3 217 5:56 1418 (24hr) 13:00 2433 (48 hr) 4 PAA 0.4 217 8:27 Not measured Not measured 5PAA 0.4 245 3:18 Not measured Not measured 6 PAA 0.4 300 1:14 Notmeasured Not measured 7 PAA 0.7 300 8:59 Not measured Not measured 8 PAA1.0 350 12:26  Not measured Not measured 9 PAA 1.2 350 16:37  Notmeasured Not measured

As can be seen in Table 2.1, for a fixed concentration of PAA, thethickening time decreases with an increase in temperature. As can alsobe seen, PAA performs comparably to the polymer conventional setretarder SCR-100™, even at lower concentrations. Also, as can be seen,at a fixed temperature, the thickening time increases as theconcentration of PAA increases.

TABLE 2.2 Set Conc. of Thickening Initial Setting Retarder set retarderTemperature Time Compressive Time Used (% bwc) (° F.) (hours:mins)Strength (psi) (hours:mins) 1 PAA 0.2 217 3:49 Not measured Not measured2 PAA 0.4 190 12:22  Not measured Not measured 3 PAA 0.4 217 9:30  461(24 hrs) 21:19 2369 (48 hrs) 4 PAA 0.4 245 4:24 Not measured Notmeasured 5 PAA 0.6 245 5:38 Not measured Not measured 6 PAA 1.0 24511:44  Not measured Not measured 7 PAA 1.2 270 3:13 Not measured Notmeasured 8 PAA 1.2 300 1:56 Not measured Not measured

As can be seen in Table 2.2, for a fixed concentration of PAA, thethickening time decreases with an increase in temperature. Also as canbe seen, at a fixed temperature, the thickening time increases as theconcentration of PAA increases.

Table 3.1 shows the fluid loss results for several cement compositions,having a density of 16.4 ppg, using two different fluid loss additives.The cement compositions consisted of the following: 5.48 gallons ofdeionized water; Class-H cement; SSA-2™ strength stabilizer at aconcentration of 35% bwc; PAA as the polymer (having an averagemolecular weight in the range of about 3,000 to about 4,000) in varyingconcentrations; and two different fluid loss additives—HALAD®344 andHALAD®413 at varying concentrations. All of the cement compositions wereheated from an initial temperature of 70° F. to a maximum temperature of190° F. over the course of 44 minutes and then maintained at thatmaximum temperature and maintained at a constant pressure of 1,000 psi.The fluid loss through the cement compositions was measured by StaticFluid Loss Test Apparatus from FANN Instruments using API recommendedprocedure and is expressed in units of total milliliters (mL) lost.

TABLE 3.1 Conc. of Conc. of Conc. of Fluid PAA HALAD ®344 HALAD ®413loss (% bwc) (% bwc) (% bwc) (ml) 1 0.3 0.5 Not Present 197 2 0.3 2 NotPresent 74 3 0.3 Not Present 2 26 4 0.3 1 1 28 5 0.4 0.5 0.5 52 6 0.4Not Present 1 92

As can be seen in Table 3.1, for a fixed concentration of PAA, theamount of fluid loss can be decreased by combining more than one fluidloss additive and also by varying the concentration of the fluid lossadditives.

The following Figures show the relationship between the concentration ofPAA/MA or PAA and either temperature or salt concentration on thethickening time of a cement composition having a density of 16.4 ppg.The cement composition included: 5.48 gallons of deionized water;Class-H cement; SSA-2™ strength stabilizer at a concentration of 35%bwc; HALAD®344 fluid loss additive at a concentration of 0.5% bwc; and apolymer. FIG. 1 is a graph of thickening time in minutes (min) versustemperature in Fahrenheit (° F.) for the cement composition at apressure of 10,200 psi wherein the polymer was PAA/MA (average molecularweight 4,500 and a mole ratio of 80:20) at a concentration of 0.4% bwc.FIG. 2 is a graph of thickening time (min) versus temperature (° F.) forthe cement composition at a pressure of 10,200 psi wherein the polymerwas PAA (average molecular weight in the range of about 3,000 to about4,000) at a concentration of 0.4% bwc. The thickening time for FIGS. 1and 2 was determined when the cement composition reached 70 Bc. As canbe seen in FIGS. 1 and 2, the thickening time decreased with an increasein temperature.

FIG. 3 is a graph of thickening time (min) versus concentration of PAA(% bwc) (average molecular weight in the range of about 3,000 to about4,000) for the cement composition at a temperature of 217° F. and apressure of 10,200 psi. The thickening time was determined when thecement composition reached 70 Bc. As can be seen in FIG. 3, thethickening time increased with an increase in the concentration of PAA.

FIG. 4 is a graph of temperature (° F.) and consistency (Bc) versus time(hrs:min) for the cement composition at a temperature of 350° F. and apressure of 10,200 psi wherein the polymer was PAA (average molecularweight in the range of about 3,000 to about 4,000) at a concentration of1.0% bwc. As can be seen in FIG. 4, it took approximately 12 hours forthe cement composition to reach at least 70 Bc at a temperature of 350°F.

FIG. 5 is a graph of thickening time (min) versus concentration ofsodium chloride (NaCl) measured as a percentage by weight of water forthe cement composition at a temperature of 217° F. and a pressure of10,200 psi wherein the polymer was PAA (average molecular weight in therange of about 3,000 to about 4,000) at a concentration of 0.4% bwc. Ascan be seen in FIG. 5, the concentration of salt affects the thickeningtime of the cement composition. Initially, as the concentration of saltincreases, the thickening time decreases. However, as the concentrationof salt continues to increase, a saturation curve can be observed.

FIG. 6 is a graph of thickening time (min) versus concentration of FAA(% bwc) (average molecular weight of 1,200) for the cement compositionat a temperature of 245° F. and a pressure of 10,200 psi. The thickeningtime was determined when the cement composition reached 70 Bc. As can beseen in FIG. 6, the thickening time increased with an increase in theconcentration of PAA.

FIG. 7 is a graph of thickening time (min) versus temperature (° F.) forthe cement composition at a pressure of 10,200 psi wherein the polymerwas the homopolymer PAA (average molecular weight of 1,200) at aconcentration of 0.4% bwc. The thickening time was determined when thecement composition reached 70 Bc. As can be seen in FIG. 7, thethickening time decreased with an increase in temperature.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is, therefore, evident thatthe particular illustrative embodiments disclosed above may be alteredor modified and all such variations are considered within the scope andspirit of the present invention. While compositions and methods aredescribed in terms of “comprising,” “containing,” or “including” variouscomponents or steps, the compositions and methods also can “consistessentially of” or “consist of” the various components and steps.Whenever a numerical range with a lower limit and an upper limit isdisclosed, any number and any included range falling within the range isspecifically disclosed. In particular, every range of values (of theform, “from about a to about b,” or, equivalently, “from approximately ato b,” or, equivalently, “from approximately a to b”) disclosed hereinis to be understood to set forth every number and range encompassedwithin the broader range of values. Also, the terms in the claims havetheir plain, ordinary meaning unless otherwise explicitly and clearlydefined by the patentee. Moreover, the indefinite articles “a” or “an”,as used in the claims, are defined herein to mean one or more than oneof the element that it introduces. If there is any conflict in theusages of a word or term in this specification and one or more patent(s)or other documents that may be incorporated herein by reference, thedefinitions that are consistent with this specification should beadopted.

1. A method for cementing in a subterranean formation, the methodcomprising the steps of: (A) introducing a cement composition into thesubterranean formation, the composition comprising: (i) cement; (ii)water; and (iii) a polymer, wherein the polymer: (a) consistsessentially of a monomer or monomers selected from the group consistingof acrylic acid, esters of acrylic acid, maleic acid, methacrylic acid,esters of methacrylic acid, itaconic acid, fumeric acid, citraconicacid, mesoconic acid, and any alkali metal, alkaline earth metal, orammonium salt of any of the foregoing, and any combination of any of theforegoing; (b) has the following characteristics: (I) is water soluble;and (II) is biodegradable; and (c) is capable of providing: (I) athickening time of at least 2 hours for a test composition maintainedunder a temperature condition of 190° F. and a pressure of 5,160 psi;and (II) an initial setting time of less than 24 hours for the testcomposition maintained under a temperature condition of 217° F. and apressure of 3,000 psi, wherein the test composition consists of 860grams of Class-H Portland cement, 325 grams of deionized water, and 0.4%by weight of the cement of the polymer, and (B) allowing the cementcomposition to set after introduction into the subterranean formation.2. The method according to claim 1, wherein the polymer is grafted ontoa backbone comprising gelatin, lignin, tannin, chitosan, cellulose, andany combination thereof in any proportion.
 3. The method according toclaim 1, wherein the cement is Class A cement, Class C cement, Class Gcement, or Class H cement.
 4. The method according to claim 1, whereinthe water is selected from the group consisting of freshwater, brackishwater, saltwater, and brine, in any combination thereof in anyproportion.
 5. The method according to claim 1, wherein the cementcomposition has a density in the range of about 9 to about 22 pounds pergallon (ppg).
 6. The method according to claim 1, wherein the polymer isa homopolymer, and the monomer is acrylic acid, maleic anhydride,itaconic acid, or methacrylic acid.
 7. The method according to claim 1,wherein the polymer is a copolymer, and wherein one of the monomers isacrylic acid, and the other monomer is selected from maleic anhydride,acrylamide, methacrylic acid, or butyl acrylate, in any proportion. 8.The method according to claim 1, wherein the polymer is in at least asufficient concentration such that the cement composition has athickening time of at least 3 hours maintained under a temperaturecondition of 217° F. and a pressure of 10,200 psi.
 9. The methodaccording to claim 1, wherein the polymer is in a concentration equal toor less than a sufficient concentration such that the cement compositionsets in less than 48 hours maintained under a temperature condition of217° F. and a pressure of 3,000 psi.
 10. The method according to claim1, wherein the polymer is in a concentration in the range of about 0.05%to about 10% by weight of the cement.
 11. The method according to claim1, wherein the polymer is in a concentration in the range of about 0.1%to about 2% by weight of the cement.
 12. The method according to claim1, wherein the polymer has an average molecular weight in the range ofabout 500 to about 5,000.
 13. The method according to claim 1, whereinthe polymer has an average molecular weight in the range of about 600 toabout 3,500.
 14. The method according to claim 1, wherein the polymerhas an average molecular weight in the range of about 800 to about2,000.
 15. The method according to claim 1, wherein the cementcomposition has a thickening time of at least 3 hours maintained under atemperature condition of 217° F. and a pressure of 10,200 psi.
 16. Themethod according to claim 1, wherein the cement composition has athickening time in the range of 4 to 10 hours maintained under atemperature condition of 217° F. and a pressure of 10,200 psi.
 17. Themethod according to claim 1, wherein the cement composition has acompressive strength of at least 400 psi when tested at 24 hours andmaintained under a temperature condition of 217° F. and a pressure of3,000 psi.
 18. The method according to claim 1, wherein the cementcomposition has a compressive strength in the range of 400 to 10,000 psiwhen tested at 24 hours and maintained under a temperature condition of217° F. and a pressure of 3,000 psi.
 19. The method according to claim1, wherein the subterranean formation contains a well.
 20. The methodaccording to claim 19, wherein at least a portion of the well has abottomhole temperature in the range of 150° F. to 400° F.
 21. A cementcomposition for use in a subterranean formation, the cement compositioncomprising: (A) cement; (B) water; and (C) a polymer, wherein thepolymer: (i) consists essentially of a monomer or monomers selected fromthe group consisting of acrylic acid, esters of acrylic acid, maleicacid, methacrylic acid, esters of methacrylic acid, itaconic acid,fumeric acid, citraconic acid, mesoconic acid, and any alkali metal,alkaline earth metal, or ammonium salt of any of the foregoing, and anycombination of any of the foregoing; (ii) has the followingcharacteristics: (a) is water soluble; and (b) is biodegradable; and(iii) is capable of providing: (a) a thickening time of at least 2 hoursfor a test composition maintained under a temperature condition of 190°F. and a pressure of 5,160 psi; and (b) an initial setting time of lessthan 24 hours for the test composition maintained under a temperaturecondition of 217° F. and a pressure of 3,000 psi, wherein the testcomposition consists of 860 grams of Class-H Portland cement, 325 gramsof deionized water, and 0.4% by weight of the cement of the polymer.